The current radiocommunication and spectrum monitoring protocols known to the applicant increasingly require a real time knowledge of the state of occupancy of the frequency bands, in order to effectively manage the allocation of the frequency bands for the users and, in the case of unauthorized presence, to be able to locate it. There are currently a number of techniques for performing a spectral analysis of a radiofrequency signal.
A first way of proceeding is to perform a multichannel spectral analysis by using filter banks. This technique presents the notable drawback of being complex to implement over wide bands. A second way of proceeding is to perform an analog spectral analysis by delay line bank. In this case, the digital metering and the standard delay line-based systems operate only in single-frequency mode. The combination of the two systems can be envisaged, but creates complexity and difficulty for the concept to be well controlled. A third alternative is to perform an analog spectral analysis by delay line with multiple taps. Finally, it is also known to use a technique known by the expression “Spectral Hole Burning” which requires cryogenics and which dictates the use of heavy, bulky and costly equipment.
Other techniques developed more recently are based on magnetic stacking structures (for example spin valves or tunnel effect metal junctions), the electrical resistance of which varies by virtue of a rectification effect upon the application of a radiofrequency wave. This characteristic variation is used to perform the real-time detection and/or spectral analysis of a given frequency range. These magnetic structures take the form of a multilayer stacking fabricated in the form of nanopillars, hereinafter “junction”. Four examples representative of magnetic structures applied to frequency detection are detailed in the patent applications: WO2006101040, US20130099339, US20080180085 and EP2515130.
Despite their performance levels, the magnetic devices proposed by the prior art allow frequency detection only above 1 GHz and with a modest resolution due to the resonance mode used (resonance mode linked to a quasi-uniform magnetization). In addition, the devices proposed are not compatible with an instantaneous wideband spectral analysis. Indeed, to cover wide bands with a single detection element, it is necessary to apply a variable magnetic field or a variable electrical current over a wide range, the detection then being done by scanning in a non-instantaneous manner. In order to lift this limitation, the patent US 20090140733 proposes a networking of multiple junctions. However, to operate, the device requires the application of a different magnetic field on each pillar. This field is then applied via a structure of “YOKE” type, known to those skilled in the art, making production extremely complex. Furthermore, one of the major benefits from this technology, which is the extreme compactness, is somewhat reduced.
In order to simultaneously address the wide band characteristic, the instantaneousness, the compactness and the detection capacity below 1 GHz, the idea of the present invention relates to a novel approach which relies on the use of a network of magnetic structures exhibiting a specific resonance mode, associated with a non-uniform magnetic configuration. In the case of a vortex magnetization, this resonance mode is the “gyrotropic mode of the vortex core”, or more simply “vortex mode”, which makes it possible to associate the oscillation frequency of a magnetic structure with its geometry.